Recycling of waste materials is highly desirable from many viewpoints, not the least of which are financial and ecological. Properly sorted recyclable materials can often be sold for significant revenue. Many of the more valuable recyclable materials do not biodegrade within a short period, and so their recycling significantly reduces the strain on local landfills and ultimately the environment.
Typically, waste streams are composed of a variety of types of waste materials. One such waste stream is generated from the recovery and recycling of automobiles or other large machinery and appliances. For examples, at the end of its useful life, an automobile is shredded. This shredded material is processed to recover some ferrous and non-ferrous metals. The remaining materials, referred to as automobile shredder residue (ASR), which may include ferrous and non-ferrous metals, including copper wire and other recyclable materials, is typically disposed of in a landfill. Recently, efforts have been made to further recover materials, such as non-ferrous metals including copper from copper wiring. Similar efforts have been made to recover materials from whitegood shredder residue (WSR), which are the waste materials left over after recovering ferrous metals from shredded machinery or large appliances. Other waste streams may include electronic components, building components, retrieved landfill material, or other industrial waste streams. These materials are generally of value only when they have been separated into like-type materials, that is, when you concentrate the copper, plastic, or other valuable materials. However, in many instances, no cost-effective methods are available to effectively sort waste streams that contain diverse materials. This deficiency has been particularly true for non-ferrous metals, including copper wiring and non-ferrous materials, such as high density plastics. For example, one approach to recycling plastics has been to station a number of laborers along a sorting line, each of whom manually sorts through shredded waste and manually selects the desired recyclables from the sorting line. This approach is not sustainable in most economics since the labor cost component is too high. Because of the cost of labor, many of these manual processes are conducted in other countries and transporting the materials to and from these countries adds to the cost.
While ferrous and non-ferrous recycling has been automated for some time, mainly through the use of magnets, eddy current separators, induction sensors, and density separators, these techniques are ineffective for sorting copper wire. Copper wiring is a non-ferrous metal that is non-magnetic and cannot be separated by magnets.
Eddy current separators create a field of energy around non-ferrous metals, which repels the non-ferrous metal. The performance of an eddy current separator depends upon the conductivity and density of the materials as well as its shape and size. An eddy current separator will perform well on a large piece of flat aluminum, but will perform poorly on small and irregularly shaped heavier metals such as copper wire.
Density separation processes typically involve expensive chemicals or other separation media and are almost always a “wet” process. These wet processes are inefficient for a number of reasons. After separation, often the separation medium must be collected, so it can be reused. Also, these wet processes are typically batch processes, such that you cannot process a continuous flow of material.
One system that can be used to identify non-ferrous metals employs standard inductive sensors. An inductive sensor consists of an induction loop. The inductance of the loop changes according to the types of material that pass inside it. Metallic materials are greater inductors than wood, plastic, or other materials typically found in a recycle waste stream. As such, the presence of metallic materials increases the current flowing through the loop. This change in current is detected by sensing circuitry, which can signal to some other device whenever metal is detected. However, inductive sensors have limitations, both in the speed that material may move passed the detector and still be detected and sensitivity to varying sizes of metallic materials.
In view of the foregoing, a need exists for cost-effective, efficient methods and systems for sorting copper wiring and other non-ferrous metals from recycle waste streams. Such methods and systems may employ sensing technology that overcomes the limitations and inefficiencies of magnets, eddy current systems, wet processes or inductive sensors.